Production of zinc oxysulfate



F 'atented July 8, 1952 lege Park, Ga., assignors ,to Tennessee Corporation, New York, N. Y., a, ;corporation of New.

York

No Drawing. J Application October 27, 1948,; Serial No. 56,908 7 V ,2 Claims. il -r This invention relates to the manufacture of zincoxy'sulphate which is especially'well suited for agricultural uses, although the product can be used for any other desired purpose.

Zinc is an essential mineral element and must beuse'd for the control of deficiency diseases in the case of various crops grown in zinc-deficient soils, It is also effective to control bacterial spot-on peaches, and acts synergistically with copper fungicides to render them-more effective. Furthermore zinc acts as a protectant or safener in sprays and dust mixtures to prevent arsenical injury to various fruits and vegetables, and in addition improves adherence.

-For these reasons zinc is an important element in agriculture. However, many readily available zinc compounds are not suitable for agricultural uses. For example, soluble zinc salts such as zincsu lphate can not be applied .directly to fruits and vegetables because of their astringent nature and harmful effect, and zinc oxide although an insoluble protectant is toxic to plant life. Hence the usual practice, has been to v treat zinc sulphate with an excess of hydrated lirne which converts the zinc sulphate into a basic or oxysulphate. 'LThe oxysulphate being only-- slightly "soluble, zinc injury is -avoided but sufficient zinc ions are liberated to produce the beneficial effects mentioned above to a substantial extent. The excesslimemaysimply be a'dded' in the spray tank or dust mixture, or ready-mixed dusts or sprays may bex.manufactured by-procedures such as disclosedin U. S. Patent No. 1,943,181. P I On theiother hand,.the presence. of excess lime in such basic zinc sulphate preparations gives rise to serious-disadvantages. f The lime carbonates on the plant and reacts with lead arsenate residues to form calcium arsenate and more soluble arsenic which may deplete the zinc safener. A" large excess of lime gives protection but forms a'thick residue that interferes with photosynthesis and weakens the plant from excessive v transpiration Moreover,: free hydrated lime causesiaconsiderable loss in efiectiveness'of certain. important insecticides T such as nicotine alkaloid (Black Leafrl55), rotenone; and organic insecticides such .as dichloro diphenyltrichlorethanelDDT),'benzene hexachloride, etc. Furthermore,.the above procedures for preparing basic zine sulphate are wasteful, and inefficientlsince a larger-partof the sulphuric acid rethe resulting product which therefore is relatively low in zinc content.

Early investigators such as Vogel, Schweigers Journal, vol. 11, 408-413 (1814) Schindler, Magazin fur Pharmacie, vol. 31, 167-186 (1830), Athanasesco, Camp. Rend., vol. 103, 271-272 (1886), and Kraut, Zeit. Anorg. ChemL, vol; 13, 1-15 (1897) reported the preparation of zinc trioxysulphate by dissolving small amounts oi.

zinc oxide in a considerable excess of boiling zinc sulphate solution. Reference to these; ar ticles shows that in each case the hot liquors were filtered and theproducts recovered by crystallization. from the cooled filtered. solutions. This method of preparation is inefficient and not adapted to commercial application;

' One of the objects of the present invention, is to provide a simple economical process for-producing zinc oxysulphate substantially free of undesirable'by-products and lime and capable of safe and efiective use for agricultural purposes such as those mentioned above without the addition ofhydra'ted lime.

Another object is to producesuch zinc oxysulphate having a relatively high zinc content, the molar ratio of zinc to sulphur being not less than'about 4:1 and preferably higher?- Still another object isitoavoid the difficulties involved in the" prior ..inefiicienttimpractical laboratory procedures mentioned above and.to form directly solid zinc oxysulphates of 4:1. @or higher ratios of zinc to sulphur by a simple practical process adapted for commercial application. Aiurther object is to complete the chemical reactions involved'and precipitate the zinc oxysulphate in a slurry that can be spray-dried. thus making it possible to eliminate filtering the slurry andwashing, drying andpulveriZing :the filtered materiaL- 7 A further object is to produce an efiective zincbearing compound which can be incorporated into dusting and spraying mixtures at the'packaging plant, thereby eliminating the dangers of omission or'improper addition to such mixtures The foregoing objectsare accomplished a novel processwherein" zinc oxysulphate'of relaquired to: a'cidulate the zinc inthe first instance is. converted into, inactive calcium sulphate, and moreover. the; latter forms, an inert diluent in tiv'ely high line content as mentioned aboveis 'formedbythe direct and substantially complete reaction water of the proper molar quantities of z nc oxide and zinc sulphate or sulphuric acid.

The reaction forms an aqueous slurry of pre- 3 erably is directly spray-dried to provide the final product.

In studying this reaction, it was found that the least basic material obtainable was zinc trioxysulphate (ratio of Zn to S= /l), and that this product could be'obtained only with suiiicient Zinc sulphate, high temperature, and prolonged reaction time. Accordingly at least three mols of zinc oxide and not more than one mol of zinc sulphate should be used for the reaction, or at. least four mols of zinc oxide and not more than one mol of sulphuric acid and further when a small amount of" calcium hydroxide is added to expedite completion of the reaction as explained hereinafter, the trioxysulphate and the heptoxydisulphate are converted to more basic sulphates such as the tetroxysulphate (ZnSO4.4ZnO.4HzO; ratio of Zn to S=5 For these reasons it is preferred to use in thepresent process not more than one mol of zinc sulphate with at least four mols of zinc oxide,.and' when the reactants are zinc oxide and sulphuric acid, the amount of sulphuric acid preferably is not more than that requiredto acidulate one-fifth or 20 per centxof the Zinc. Still lesser amounts of sulphuric acid (or zinc sulphate) may be employed. to produce oxysulpha'tes of still higher zinc content such as the pentoxy and heptoxy sulphates as explained hereinafter. e

Boiling temperatures can. be used but best results are obtained with temperatures not greater than 190 F., the preferred temperature range'being 160-190 F. Lower temperatures can be used'down to about 120 F., but. the required reaction time will. be correspondingly increased. I

The amount of water is not critical but preferably. shouldlbe' enough .to provide. a fairly dilute slurry in the neighborhood of;25%. solids by weight at the start of the reaction. ..The. upper limit of solids is the pointat which. the slurry becomes too thick during the course of...the reaction fori 'effe'ctive,agitation, which may. take place if thesolids content at the, start of the reaction; is greater than :30.-35 More. .dilute slurriescan be used but. are. disadvantageous because of slower .lreactiom .and s also. because in case of spray drying...there .is acorrespondingly larger quantityzof waterto beremoved;

Assuming. the use of molar. quantities... of zinc oxide and sulphuric acid such as; to produce the However, higher zinc content is desirable for agricultural uses,.

4 12 to 24 hours by which time the pI-I of the slurry will have increased to about 6.45-6.50, the pH determinations being made on the slurry cooled to a uniform temperature of 75 F. without removing solids. If the reaction is stopped at this point, which will be convenient in most cases, there will still be around 7-8%.1of the original zinc sulphate remaining in soluble form with resulting danger of injury to the plant if the .dried product should be used for agricultural purposes. To avoid this danger, the slurry may be filtered'and the filter cake washed to remove remaining soluble zinc, after which the washed filter cake canbe dried and pulverized or reslurried and spray dried. On the other hand, the reaction, can be carried substantially to completiori if enough time is allowed, at which point tetroxysulphate, the, process. may.:-;be-; carried, out 1 very simplyjand effectively diluting; one... mol of sulphuric acid, with, part or the calculated amount of water,.preparingav slurry containing five mols of zincoxidewith the. restxofthe water, mixing the two and heating thegmixture with agitation atatemperature of 18 O 19Q F. The extent of dilution of thesulphuric acid andv the degree of concentration of the zinc oxide-slurry may-vary within wide limits, provided thetotal amount of water. conforms} to L the conditions prescribed above V v The sulphuricacid reacts with ,oneefif'th of the zinc oxide to f orm ,1 mol'of zinc;sulphate,which in turn reacts with the remainin'gIfo-ur mols of zinc oxide'to "form' the tetroxysulphate; Hence it will beunderstood that if desired, the starting materials may be 1 mol of zinc sulphate and four mols of zinc-oxide.

The reaction-"proceeds rapidly at ;-becomes progressively slower, reaching-about 98%. completion under the above conditionsin' the slurry will be approximately neutral (pH 6.8 or 6.9). In this case the slurry can be filtered and dried without washing, or preferably is directly spray dried.

To eliminate washing and atthe'same. time avoid prolonging the time of the reaction,- however, enough alkali is preferably addedtoyprecipitate substantiallyall of the remaining soluble zinc. Hydroxides of any alkali oralkaline earth can be used for this purpose; The amount of by product sulphate thus formed is so;sm all that it does not dilute the resulting product materially, and can be allowed to remain in the product even for agricultural purposes since it is prace tically harmless in such small amounts, Hence the'finished slurry ispreferably directlyrspray dried to obtain oxysulphate We prefer to use calcium hydroxide for the above purpose because it is economical and; the by-product calcium sulphate is non-injurious. When calcium hydroxide is used in the above manner to precipitate substantially all; of; the soluble zincremainingat the end of the reaction described above, the product will range fromthe tetroxysulphate to the pentoxy sulphate in com; position as illustrated by the examples set forth below.

The? elimination of the steps offi-ltering, wash: ing, drying and grinding and the substitution of a; simple spray drying. operation are; important advanta'gesfof the. invention. The realization: of these advantages is due in part to the finely divided granular character. of the solids andto the absence of harmful amounts of'solublebyr productsulphates in the accompanying, liquors; In contract,: zinc oxysulphates as; ordinarily prepared in quantity by the action oflalkalion zinc sulphate are precipitatedasgelations, slimy solids in the. presence of a considerable concen-z tration of harmful soluble sulphates. from which they must be separated. byfiltrationandwashing. These gelatinous precipitates arediificult to filter andwash, and when dried are, tough and very difiic'ult to grind; furthermore, such filtered and washed products aredifliculttodisperse. and hence are not suitable forspray drying- The finely divided granularprecipitates ob-. tained by the present invention are. easilytfiltered, washed, dried and pulverized, or easily; spray dried. Moreover, these precipitatesidolnot con-.- tain'objectionable impuritiesin the .form'ofleither unreacted materials .orbyT-products andihence the slurries can bespray dried directly. I

Higher basic products can be obtained .by stopping the reaction'before therpoint mentioned above. is reached." However, when the product is. intended for agricultural use, thepH iofe the reaction. mixture should. be allowed to increase a relativelylarge amount. of by-product sulphate whichis'undesirable for many purposes. Furthermore, products of the order of the heptoxysulphate can be formed rapidly by adjusting the molar quantities of the reactants to satisfy, this relation. The basicity of the final-product can also be increased :by. adding sufiicient calcium hydroxide or the like" at the end of the reaction to bring the pH to approximately 8.0 or higher.

A specific example of the present process, basedon the use of the preferred molar proportions stated above, is as follows:

One hundred pounds of zinc oxide (81.3% Zn) were slurried with 135 lbs. or22 gallons of water to provide a slurry containing 35% solids by weight. The amount of H2304 required tov combine with one-fifth or'16.3' lbs. of the zinc was 24.5 lbs. which was equivalent to 122.5 lbs. of 20% acid. This dilute acid solution was --made up-by diluting 31.5 lbs. o f 60f-;Be. acid with 90.5 lbs. or 10.9 gallons o'f waten making a total volume of 12.8 gallons.

The zinc oxide slurry was added slowly to the dilute acid, the total volume of the mixture including rinsings being approximately 43.5 gallons. This mixture was agitated at 180-l90 F. until a pH of 6.45-6.50 was reached, the time required being about 15 hours. At this point about 7% or 1.2 lbs. of soluble zinc remained unprecipitated. The slurry was approximately 92% solution and 8% solids by volume or 28% solids by weight. The apparent volume of the solution was 43.5 gallons.

At this stage the slurry can be filtered and the 6 6.45-6.50. was about 3.5 grams per liter '01003 lb. per gallon. The total amount of soluble zinc was then calculated by multiplyingithese amounts by the apparent'volume of the solution and by thev factor 0.92 representing the approximate actual volume of the solution. *With an apparent volume of 43.5 gallons as in the above example, the calculated amount of soluble zinc remaining in solution was 1.165lbs. and the required amount ofcalcium hydroxide calcu lated to form tetroxysulphate was 1.06' lbs.

Equivalent amounts of lime (allowing for any 1 CaCOa present in the lime) were dispersed .in about 2 gallons of water which were added to the reaction tank at a uniform rate over a period of about five minutes to avoid high concentration of limeina limitedpart of the slurry. The slurry was agitatedwhile its pH rose slowly to 7.0,by which time the soluble zinc content had decreased to about 0.35 gram per .liter, 99% of thesoluble zinc had been precipitated, and over99.9%:'-of the total..zinc .was; in insoluble form. Such slurries. can be...filtered,v dried andi'pulv'eri'zed without washing, or they can be .directly spray dried.

The following table gives the analyses ofa number of products prepared according: to. the procedure of the above example; In most of these tests the slurry was cooled to 80-100 .F. before completing precipitation with calciumliydroxide,in order to accomplish this final precipitation faster andwith-a minimumgofside reaction to higher oxysulphates and consequently a minimum consumption of lime. The table shows the results obtained when the precipitated solids were filtered, washed and dried without adding lime (see A samples) and when precipitation was completed by adding line to pH 'LO (see B, samples). The oxysulphates thus obtained ranged in composition from the tetroxy to the pentoxy sulphate (ratio of Zn to S from 5/1 to 6/1). However, field tests of agricultural sprays and dusts containing oxysulphates varying in composition within this range disfilter cake washed free of soluble sulphates in a closed no difference in their effectiveness.

Per Cent Zn Per Cent 8 M01. Zn

Per Cent Batch No. 08304 Total 801 Total FN,HF N F F.P PP quomwowcwomowcwwo amummamummmuummuu FPH99WWSPWFPHPFPW mmqoamowmpwawaoog 99999999999999 Mmwwwwwmmwww u come mcmoooc m PPPPPPPPPPPPF 'wwwwwwwawa A--Precipitated solids before adding lime filtered, washed and dried).

B-Precipitated solids after adding lime tered and dried cake).

1 This ratio is based on the water-insoluble quantities.

filter press. The remaining product can either be dried and pulverized, or reslurried and spray amount of soluble zinc left in solution at pH 75 Apart from the important procedural advantages mentioned above, the product obtained by the foregoing process is exceptionally well suited for agricultural uses because of its high zinc content and very low content of water-soluble zinc as indicated in the above table, and because it is free of by-products harmful to plant life and can be used without the addition of lime.

It will be understood that the invention is not 7. restricted; to the details set forth above by tvay ofgiexample and; thatreference should be had to thezaplqendediclaims for a definition of its limits.

:Whatis claimed-is: i. a

.1. The; method; ofymaking a zinc product: partieularly adapted for. agricultural: uses and con-; sisting essentially of zinc.oxysulphateyhaving; a molar ratio of approximately 5.0-5.5. parts of zinc toone' part of sulphur which comprises forming; anaqueous slurry containing. approximately five mols of zincqoxideiormingan aqueous solu.-. tion containingapproximately one :mol of Sui-'- phuric. acid, adding the-zinc oxidev slurry to the acid solution: and agitating the gmixture while maintaining a reaction"'temperature of about 180+190 E1until the pH of'the mixture-increases t0--abouti6.0',6;5., the. amount of solids in said mixture being. about.25-.35% by weight, thereby precipitating s'aid zinc oxysulphate. in the hot mixturesin finely=;divid'ed form, then'cooling' the mixtureto about 80-1001F;, then adding tothe mixtureaan amounto'f calcium hydroxide sufficienti to precipitate the zinc: remaining insolution; and;then spray drying the mixture.

2. The method of making a zinc product consisting essentially of zincoxysulphate having a molar ratio of approximately 5.0-5.5 parts of zinc to one part of sulphur (which comprises forming an aqueous slurry. containing zinc oxide and zinc sulphatein the approximate proportions offour 1-.

trials of zinc oxide to one mol ofzinc sulphate, the maximum-solids-content of said' slurry being REFERENCES CITED The following referencesfare of record in the.

file or: this patent: I

UNITED 'SV'IATESQPAV'IEN'IS Number Name W Date I 1,074,203;- Rees et at].. Sept. 30, 1.913 1,204,843 Bretherton Nov. 14, 1916 1,906,074 Mertes Apr. 25 1933 1,912,332 Steinbring May- 30, 1933 FOREIGN PATENTS Number Country Date Great Britain V Mar. 20; 1930 OTHER REFERENCESiI MelIor, Comprehensive Treatise on Inorganic and TheoreticaPChemistry; vol. 4, Longmans Green a 00;, N; Y; (1923), pages-625-626. 

1. THE METHOD OF MAKING A ZINC PRODUCT PARTICULARLY ADAPTED FOR AGRICULTURAL USES AND CONSISTING ESSENTIALLY OF ZINC OXYSULPHATE HAVING A MOLAR RATIO OF APPROXIMATELY 5.0-5.5 PARTS OF ZINC TO ONE PART OF SULPHUR WHICH COMPRISES FORMING AN AQUEOUS SLURRY CONTAINING APPROXIMATELY FIVE MOLS OF ZINC OXIDE, FORMING AN AQUEOUS SOLUTION CONTAINING APPROXIMATELY ONE MOLE OF SULPHURIC ACID, ADDING THE ZINC OXIDE SLURRY TO THE ACID SOLUTION AND AGITATING THE MIXTURE WHILE MAINTAINING A REACTION TEMPERATURE OF ABOUT 180*-190* F. UNTIL THE PH OF THE MIXTURE INCREASES TO ABOUT 6.0-6.5, THE AMOUNT OF SOLIDS IN SAID MIXTURE BEING ABOUT 25-35% BY WEIGHT, THEREBY PRECIPITATING SAID ZINC OXYSULPHATE IN THE HOT MIXTURE IN FINELY DIVIDED FORM, THEN COOLING THE MIXTURE TO ABOUT 80*-100* F., THEN ADDING TO THE MIXTURE AN AMOUNT OF CALCIUM HYDROXIDE SUFFICIENT TO PRECIPITATE THE ZINC REMAINING IN SOLUTION, AND THEN SPRAY DRYING THE MIXTURE. 